Driver testing

Manual hardware unit tests

A driver may choose to implement the run_unit_tests() driver op, which provides the driver a hook in which it may run unit tests at system initialization with access to the parent device. This means the driver may test its bind and unbind hooks, as well as any interactions with real hardware. If the tests pass (the driver returns true from the hook) then operation will continue as normal and bind() will execute. If the tests fail then the device manager will assume that the driver is invalid and never attempt to bind it.

Since these tests must run at system initialization (in order to not interfere with the usual operation of the driver) they are activated with a kernel command line flag. To enable the hook for a specific driver, use driver.<name>.tests.enable. Or for all drivers: driver.tests.enable. If a driver doesn't implement run_unit_tests() then these flags will have no effect.

run_unit_tests() passes the driver a channel for it to write test output to. Test output should be in the form of fuchsia.driver.test.Logger FIDL messages. The driver-unit-test library contains a helper class that integrates with zxtest and handles logging for you.

Integration tests

Driver authors should use the driver_test_realm for integration tests.

Unit tests

Drivers authors should use the mock-ddk library for unit tests.

There are a number of helpful mock libraries:

TODO( Fill out more detail here.